Spectrally sensitized direct positive silver halide emulsion layers

ABSTRACT

Photographic direct positive silver halide emulsions are spectrally sensitized having a thiazole ring which is connected in 5-position through a methine chain to a 5- or 6-membered heterocyclic ring.

United States Patent [191 Dhlschliiger et a1.

1 1 SPECTRALLY SENSITIZED DIRECT POSITIVE SILVER HALIDE EMULSION LAYERS [75] Inventors: Hans Ohlschliiger,

Bergisch-Gladbach Schildgen; Oskar Riester; Alfons Dorlars, both of Leverkusen, all of Germany [73] Assignee: AGFA-Gevaert Aktiengesellschaft,

Leverkusen, Germany 22 Filed: June 28,1972

211 App]. No.: 267,165

[30] Foreign Application Priority Data July 2, 1971 Germany 2132937 [52] US. Cl. 96/101, 96/130, 260/240 R [4 1 June 11, 1974 Primary ExaminerJ. Travis Brown Attorney, Agent, or FirmConno11y and Hutz [57] ABSTRACT Photographic direct positive silver halide emulsions are spectrally sensitized having a thiazole ring which is connected in 5-position through a methine chain to a 5- or 6membered heterocyclic ring.

2 Claims, 7 Drawing Figures SPECTRALLY SENSITIZED DIRECT POSITIVE SILVER HALIDE EMULSION LAYERS The invention relates to photographic direct positive silver halide emulsions which are sensitized with special cyanine dyes.

Numerous sensitizing dyes are known for the usual negative silver halide emulsions, e.g. monoor trimethine cyanines, merocyanines or rhodacyanines.

The known sensitizing dyes, however, cannot usually be used for sensitizing direct positive emulsions, i.e. emulsions which are processed to produce positive images after the usual exposure and development, because they generally cause flattening of the 'y-value or gradation. On the other hand, compounds have already been described which are only suitable as sensitizing dyes for direct positive emulsions. If used in negative emulsions, these compounds cause fogging and their sensitizing effect is unsatisfactory. lndocyanines are examples of sensitizing dyes which have been used for direct positive emulsions. Although these have a quite advantageous effect on the sensitivity of the emulsions to the red region of the spectrum, their sensitizing effect is still not completely satisfactory. This also applies to the direct positive indole sensitizing dyes for the green region of the spectrum and to bis-thiazol and bisselenazolyl compounds which are known as sensitizers for direct positive emulsions.

It is among the objects of the present invention to provide sensitizing dyes for direct positive silver halide emulsions which have a sufficiently intense sensitizing effect and do not adversely affect the gradation.

We now have found that cyanine dyes which have a thiazole nucleus whose carbon atom in the 5-position is connected via a methine chain to a second nucleus of the type usually present in known cyanine dyes, are highly effective cyanine dyes, suitable for the preparation of direct positive photographic silver halide emulsions. The new cyanine dyes are particularly suitable as so-called electron acceptors and spectral sensitizers for developable fogged silver halide emulsions. They produce both excellent general speed and a selective sensitivity to light from the green and red regions of the visible spectrum. Images obtained with such silver halide emulsions are exceptionally clear and sharp and have excellent contrast. The second nucleus which is connected to the thiazole nucleus by a methine group may be a 5or 6-membered nitrogen containing nucleus of the type normally found in known cyanine dyes.

Particular utility is exhibited by cyanine dyes characterized by one of the following formulae 1 or II:

hydrocarbon group which preferably contains up to 6 carbon atoms and may be substituted, e. g. with phenyl, hydroxyl, halogen, carboxyl, sulfo, carbon- .amido, carbalkoxy, sulfato or thiosulfato, sulfonamido or phosphato; (2) cycloalkyl such as cyclohexyl, or (3) aryl, particularly phenyl;

R, R, R stand for (1) hydrogen, (2) saturated or unsaturated aliphatic groups preferably containing up to 6 carbon atoms, for example methyl or ethyl, or (3) aryl, for example phenyl which may be substituted, for example with alkyl, or alkoxy;

R R", R represent (1) hydrogen, (2) saturated or unsaturated aliphatic groups preferably containing up to 3 carbon atoms, for example methyl or ethyl, (3) aryl, for example phenyl, or (4) carbalkoxy such as carbethoxy, and R and R may also together represent the ring members required for completing a condensed benzene or naphthalene ring;

R", R R represent l) saturated or unsaturated aliphatic groups preferably containing up to 6 carbon atoms, for example methyl or ethyl, or 2) aryl, forexample phenyl; R and R may also together represent the ring members required for completing a heterocyclic ring, e.g. for completing a pyrrolidine, piperidine, morpholine or thiomorpholine,

indoline or tetrahydroquinoline ring;

n 0 or 1,

m O or 1,

Anion 8 represents any anion, e.g. a halide such as chloride, bromide or iodide, perchlorate, sulfate, methylsulfate, p-toluenesulfonate, acetate or oxalate; the anion is absent in cases where R or R contains an acid group in the anionic form so that a betaine is present;

Z represents a radical required for completing a heterocyclic group containing a 5 or 6-membered heterocyclic ring; the heterocyclic group may contain a condensed benzene or naphthalene ring and other substituents; the heterocyclic groups are those commonly used in cyanine chemistry, for example those based on thiazole, (e.g. thiazole, 4- methylthiazole, S-methylthiazole, 4,5- dimethylthiazole, 4-phenylthiazole, 5- phenylthiazole or 4,5-diphenylthiazole), benzothiazole, (e.g. benzothiazole, 4-chlorobenzothiazole,

5-chlorobenzothiazole, -chlorobenzothiazole, 7- chlorobenzothiazole, 6-bromobenzothiazole, 5- iodobenzothiazole, 6-iodobenzothiazole, 4- me'thylbenzothiazole, S-methylbenzothiazole, 6- methylbenzothiazole, 5,6-dimethylbenzothiazole, 4-phenylbenzothiazole, S-phenylbenzothiazole, 6- phenylbenzothiazole, S-hydroxybenzothiazole, 6- hydroxybenzothiazole, S-ethoxybenzothiazole, 6- ethoxybenzothiazole, 5,6-dimethoxybenzothiazole, 5,-methylene-dihydroxy-benzothiazole, 5- diethylaminobenzothiazole, 6- diethylaminobenzothiazole, 6-cyanobenzothiazole, S-carboxybenzothiazole, 5-sulfobenzothiazole, tetrahydrobenzothiazole or 7-oxotetrahydrobenzothiazole), naphthothiazole (e. g. napthol l ,2 d ]thiazole, naphtho[ 2, l -d ]thiazole, 7- methoxynaphtho[2,l-d]thiazole or 8- methoxynaphtho l ,2-d]thiazole), selenazole (e.g., 4-methylselenazole or 4-phenyl-selenazole), benzoselenazole (e.g. benzoselenazole, 5- chlorobenzoselenazole, 5,6-dimethylbenzoselenazole, S-hydroxybenzoselenazole, 5- methoxybenzoselenazole or tetrahydrobenzoselenazole), naphthoselenazole (e.g. naphtho[ 1 ,2-d]selenazole or naphtho-[ 2, l d]selenazole), oxazole (e.g. oxazole, 4- methoxyoxazole, 4-phenyloxazole or 4,5- diphenyloxazole), benzoxazole (benzoxazole, 5- chlorobenzoxazole, 6-chlorobenzoxazole, 5,6-dimethylbenzoxazole, S-phenylbenzoxazole, S-hydroxybenzoxazole, S-methoxybenzoxazole, 5- phenylbenzoxazole, S-hydroxybenzoxazole, 5- methoxybenzoxazole, S-ethoxybenzoxazole, 6- dialkylaminobenzoxazole, S-carboxybenzoxazole, 5-sulfobenzoxazole, sulfonamidobenzoxazole, or 5-carboxyvinylbenzoxazole), naphthoxazole (e.g. naphtho[ l,2-d]oxazole, naphtho[2, l -d]oxazole or naphtho [2,3-d]oxazole), imidazole (e.g. lmethylimidazole, l-ethyl4-phenylimidazole or 1- butyl-4,S-dimethylimidazole), benzimidazole (e.g. l-methylbenzimidazole, l-butyl-4- methylbenzimidazole, l-ethyl-5,6- dichlorobenzimidazole or l-ethyl-S-trifluoromethylbenzimidazole), naphthimidazole (eg 1- methylnaptho[ l,2-d]imidazole or lethylnaphtho[2,3-d]imidazole), 3,3- dialkylindolenine (e.g. 3,3-dimethylindolenine, 3,3,5-trimethylindolenine or 3,3-dimethyl-5- methoxyindolenine), 2-pyridine (e.g. pyridine, 3- methylpyridine, 4-methylpyridine, 5- methylpyridine, 6-methylpyridine, 3,4- dimethylpyridine, 3,5-dimethylpyridine, 3,6 -dimethylpyridine, 4,5-dimethylpyridine, 4,6- dimethylpyridine, 4-chloropyridine, 5- chloropyridine, 6-chloropyridine, 3-

hydroxypyridine, 4-hydroxypyridine, 5- hydroxypyridine, 3-phenylpyridine, 4- phenylpyridine or 6-phenylpyridine), 4-pyridine (e.g., 2-methylpyridine, 3-methylpyridine, 2,3- dimethylpyridine, 2,5-dimethylpyridine, 2,6- dimethylpyridine, 2-chloropyridine, 3- chloropyridine, Z-hydroxypyridine, or 3- hydroxypyridine), 2-quinoline (e.g. quinoline, 3-

methylquinoline, S-methylquinoline, 7- methylquinoline, 8-methylquinoline, 6- chloroquinoline, 8-chloroquinoline, 6- methoxyquinoline, 6-ethoxyquinoline, 6-

hydroxyquinoline, S-hydroxyquinoline or 5-oxo- 5,6,7,8-tetrahydroquinoline), 4-quinoline (e.g. quinoline, 6-methoxyquinoline, 7-methylquinoline or 8-methylquinoline), isoquinoline (e.g. isoquinoline or 3,4-dihydroisoquinoline), thiazoline (e.g. thiazoline or 4-methylthiazoline), and those based on pyrroline, tetrahydropyridine, thiadiazole, oxadiazole, pyrimidine, triazine or benzothiazine and pyrimidone or thiopyrimidone. The aryl groups and heterocyclic groups may carry any other additonal substituents, e.g. alkyl, preferably withup to 3 carbon atoms such as methyl or ethyl, halogen such as chlorine or bromine, hydroxyl, alkoxy preferably with up to 3 carbon atoms such as methoxy or ethoxy, hydroxyalkyl, alkylthio, aryl such as phenyl, aralkyl such as benzyl, amino, substituted amino or nitro.

The following are examples of suitable compounds.

Absorption Sensitization maximum maximum No. Dye (nm.) (n.rn.) 1 s\ s 454 530 JH=0H SCH i 3 6m N J O2N s 47 550 -oH=cH- l SCH3 I (III-13$ N J CH=CH -SCH;

N H30 l e; N 9

s L CH-CH s N/ g SCH; (311, mo-

1130* (DMSO) 0 CH=CH Absorption Sensiti zation maximum maximum No. Dye (nm.) (nm.)

S (Aceton) H5O --CH=CH}/ N w (11H; N

as e53 120 on C--CH=CH 3 ll \N @w 3m 0104 OzN S CH=CH $6) N CH:

HrC-N (DMSO) S v s CH=CH N l HaC-N s 0 CH=CH l e l N/ CH3 N/ CH3 H3CN/\] (Aceton) s s=L CH=0HT N 69 l (17H; cm

as s 540 605 OzN- 8 (DMSO) CH=CH Q l N N (g 6 N I The new cyanine dyes of the above formula I can easily be obtained by reacting a heterocyclic compound of 5 5 the following formula Ill:

Hit.

wherein I R, n, 2 and anion have the meaning already indicated and R represents a methyl group,

with

wherein fore.

Anion a thiazolealdehyde of the structural formula IY 65 R and R have the meanings mentioned herein be- The reaction is preferably carried out at temperatures of between 15C. and the reflux temperature of the mixture, preferably using equimolar or approximately 9 60 equimolar ratios. The reaction may be carried out in the presence or absence of a condensing agent, for example a trialkylamine, in an inert solvent, for example an alkanol, erg. ethanol, or acetic acid anhydride.

The dyes of Formula II are obtained by condensation of a pyrrole or indole of Formula V:

Leela];

13 wherein R, R R R, R and m have the meanings already indicated with an aldehyde of formula IV with the addition of at least 1 mol of an acid, e.g. acetic acid. The condensation may advantageously also be carried out in glacial acetic acid with the addition of a condensing agent such as phosphorus oxychloride. The thiazole aldehydes of formula IV are easily obtained from the corresponding thiazoles by the Vilsmeier reaction as described in German Pat. Specification Nos. 1,137,024 and 1,147,584.

The preparations of dyes l, 8 and 10 are described in detail below: Dye 1 3.3 g of 2-methyl-3-ethyl-benzothiazolium-tosylate and 1.4 g of 2-methylmercapto-4-phenylthiazolealdehyde-S in 20 ml of acetic acid anhydride are heated under reflux for 10 minutes. The solution is cooled and the dye is precipitated with potassium iodide solution, filtered under suction and recrystallized twice, each time from 100 ml of methanol, with the addition of active charcoal. 1,4 g of dye of melting point 228C (decomposition) is obtained.

Dye 8 2.4 g of 1,3,6-trimethyl-Z-oxo-pyrimidinium perchlorate and 2.3 g of 2-dimethylamino-4-phenyl-thiazolealdehyde-5 in 20 ml of acetic acid anhydride are heated under reflux for minutes. The dye precipitates after heating for a short time. The mixture is cooled and the dye is filtered under suction and recrystallized from 250 ml of glacial acetic acid.

Yield 4.2 g, mp: 277C (decomposition).

Dye 10 2.0 g of 1-methyl-2-phenyl-indole and 3.0 g of 2- methyl-phenylamino-4-phenyl-thiazole-aldehyde-5 in 10 ml of glacial acetic acid with the addition of 2 ml of phosphorus oxychloride are heated under reflux for one hour. The dye solution is cooled and the dye is precipitated with sodium perchlorate solution, filtered under suction and recrystallized from 150 ml of alcohol.

Yield 1.6 g, m.p.: 160 162C.

The dyes used according to the invention generally have no sensitizing effect in conventional negative emulsions but on the contrary reduce the overall sensitivity and reinforce the unwanted uniform grey fog. In direct positive emulsions, on the other hand, these dyes have a spectral sensitizing effect resulting in exceptionally high sensitivity and excellent steepness of the gradation.

According to a particularly preferred embodiment of the invention, the new cyanine dyes are used for the preparation of direct positive photographic silver halide emulsions, in particular developable fogged silver halide emulsions. The emulsions may be fogged by the usual methods, for example by the action of light or socalled chemical fogging agents, for example stannous chloride, formaldehyde, thiourea dioxide. Another advantageous method of fogging the emulsions consistsin adding a reducing compound, for example thiourea dioxide, and the compound of a metal which is more electropositive than silver, for example a gold salt, e.g., potassium chloroaurate, as described in British Pat. Specification No. 723,019.

Typical reducing compounds which are suitable for preparing such fogged silver halide emulsions are, for

example stannous salts, such as stannous chloride, hy-

drazine, sulfur compounds such as thiourea dioxide, phosphonium salts, e.g. tetra-(hydroxymethyD- phosphonium chloride. Typical compounds of metals which are more electropositive than silver are, for example compounds of gold, rhodium, platinum, palladium and iridium. [t is preferred to use soluble salts of the said noble metals, e.g. potassium chloroaurate, auric chloride and (NH PdCl The concentration of the reducing agents or the compounds of the metal which is more electropositive than silver, used for fogging can vary within wide limits. In general, concentrations of 0.0005 to about 0.06 milliequivalents of reducing agent and about 0.001 to about 0.01 milli-mols of the noble metal salt per mol silver halide have proved sufficient.

Fogging can be also accomplished with the method of silver halide digestion described by WOOD in .l.phot.Science" l (1963) page 163, at pAg values between 2 and 5 and pH values of about 6.5.

Any type of direct positive photographic emulsions can be spectrally sensitized by the sensitizing dyes of the present invention. Suitable direct positive emulsions include silver halide emulsions the grains of which have high internal sensitivity in particular silver halide emulsions containing internal electron traps. Particular utility is exhibited by direct positive silver halide grains comprising a central core of a silver halide which contains centres which act as electron traps and an outer shell covering said core comprising a fogged silver halide that develops to silver without exposure. Emulsions of that type are disclosed by E. MOlSAR and F. WAG- NER in lilericlite der Bunsengesells cliaft fiir physikalische Chemie 67 (1963), pages 365 359. We furthermore refer to British Pat. Specification Nos. 1,027,146 and 1,151,781 or to French Pat. specification No. 1,585,791. The formations of the centres or specks in the inside of the grains particularly on the core of the composite grain are produced as known per se by chemical sensitizing the emulsions with compounds of nobel metals in particular gold or iridium salts are sulfur compounds such as thiosulfates. In particular useful is a treatment with noble metal salts and sulfur compounds.

The spectral sensitizers of the present invention can also be applied to direct positive emulsions which are fogged on the surface so that they can be developed to silver without exposure and which contain at the surface electron acceptors such as desensitizing dyes. Suitable dyes for this purpose are well-known. Reference is made, e.g., to pinacryptol yellow or nitro-substituted polymethine dyes. The technic of desensitization and the chemical structure of suitable desensitizing dyes are described, e.g., by O. RIESTER in Mitteilungen aus den Forschungslaboratorien der Agfa, Volume 1 (1955), page 44 or in the handbook Grundlagen der photographischen Prozesse mit Silberhalogeniden," Volume 3, page 1077. The direct positive sensitizing dyes of the present invention can be used in combination with further sensitizing dyes capable of sensitizing direct positive emulsions and desensitizing negative silver halide emulsions as described for example in US Pat. Nos. 3,314,796 or 3,505,070. Further suitable direct positive emulsion are described in German Pat. specification Nos. 606,392 or 642,222 or in UK Pat. specification Nos. 581,773 or 655,009.

The direct positive emulsions may also contain mercury salts and thallium salts as described in British Pat. specification No. 1,203,744 or US. Pat. spec. No. 3,620,750.

The silver halide of the silver halide emulsions to which the new cvanine dves may be added may consist of one of the usual silver halides used for preparing photographic silver halide emulsions, i.e. for example silver bromide, silver iodide, silver chloride, silver chlorobromide, silver bromoiodide and silver chlorobromoiodide.

The new dyes may be incorporated with silver halide emulsions at the usual concentrations, for example concentrations of about 50 to 2.000 mg, preferably about 400 to 800 mg/mol of silver halide.

The new cyanine dyes are preferably added to the washed, prepared silver halide emulsions and dispersed in them as uniformly as possible. The incorporation of the dyes in the emulsions may be carried out by the usual known methods, for example the dyes may be added to the emulsions from solutions in suitable solvents. The solvent must, of course, be selected so that they have no adverse effect on the light-sensitive photographic material which is to be produced. Suitable solvents are, for example, methanol, isopropanol, acetone and water, either separately or mixed with each other.

The binder of the silver halide emulsions to which the cyanine dyes according to the invention may be added may be any of the hydrophilic colloids commonly used for the preparation of photographic silver halide emulsions, for example naturally substances such as proteins, in particular gelatin, albumin, agar-agar, gum arabic or alginic acid or synthetic hydrophilic resins such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose ethers or partly hydrolyzed cellulose acetate.

The emulsions containing one or more cyanine dyes according to the invention may be applied to the usual opaque or transparent photographic supports used for the preparation of photographic materials, for example supports of glass, cellulose acetate, cellulose acetobutyrates or polyesters, e.g., polyethylene terephthalate, or supports of baryta-coated paper or paper coated with polyolefines such as,polyethylene.

The photographic silver halide emulsions to which the new cyanine dyes are added, as well as the other layers of a photographic material which is prepared using these emulsions may be hardened by the addition of the usual hardeners such as aldehyde hardeners, e.g. formaldehyde or mucochloric acid.

The good sensitizing effect is preserved even in the presence of water-soluble and emulsified color couplers. The emulsion may also contain the usual wetting agents, stabilizers, brightening agents and other additives.

EXAMPLE 45 mg of Dye 3 in the form of a 121000 solution in methanol are added with stirring to 1 kg of a direct positive emulsion which has been fogged by chemical fogging with ammonia and excess silver nitrate and which contains 0.4 mol of silver halide per kilogram of casting solution with an iodine content of 2.5 mol percent, based on the amount of silver, and the mixture is left to digest for 10 minutes. 10 ml of a 4 percent solution of saponin as wetting agent and ml of a 5 percent solution of mucochloric acid are then added.

The emulsion is then cast on a cellulose acetate support in the usual manner. When dry, the layer is exposed to white light in a sensitometer and developed for 5 minutes at 20C with a developer of the following composition:

made up to l litre with water.

The emulsion is then fixed in the usual manner. A positive image of the step wedge with exceptional clear whites and excellent gradation is obtained. The spectral sensitization curve is shown in FIG. 2. FIG. 1 shows for comparison the sensitivity curve obtained without a sensitizer.

If Dye 3 is replaced by an equal quantity of Dye 11, the sensitization curve shown in FIG. 3 is obtained, and if with an equal quantity of Dye 12, the sensitization curve shown in FIG. 4 is obtained. Using the same photographic process, the sensitization curves shown in FIGS. 5, 6 and 7 are obtained using Dyes 13, 31 and 34.

We claim:

1. A photographic material comprising at least one direct positive fogged silver halide emulsion layer, which contains one of a sensitizing cyanine dye of the following formulae:

R represents an aliphatic group having up to 6 carbon atoms, cycloalkyl or aryl;

R R and R represent hydrogen, an aliphatic group having up to 6 carbon atoms or aryl;

R R and R represent hydrogen, an aliphatic group having up to 3 carbon atoms, aryl or carbalkoxy; or R and R may together represent the ring members required for completing a condensed benzene or naphthalene ring;

R", R and R stand for an aliphatic group having up to 6 carbon atoms;

n is O or I;

m is 0 or 1;

Anion represents an anion but is absent when R or R contains an acid group in the anionic form so that a betaine is present;

Z stands for a radical required for completing a heterocyclic ring selected from the group consisting of benzothiazole, pyrimidone, thiopyrimidone, indolenine, benzoxazole, imidazoquinoxaline, quinoline, thiazolo pyrimidine, benzthiazolo pyrimidine, pyridino pyrimidine, oxadiazole, thiazoline and oxazoline.

2. The material of claim 1, wherein Z represents the ring members required for completing one of the following rings: benzothiazole, pyrimidone, thiopyrimidone, indolenine. 

2. The material of claim 1, wherein Z represents the ring members required for completing one of the following rings: benzothiazole, pyrimidone, thiopyrimidone, indolenine. 